The present invention relates to an apparatus for determining the temperature of a substrate, in particular a semiconductor substrate, as well as to an apparatus and a method for thermally treating substrates, in particular semiconductor substrates.
In the art, different apparatuses and methods for thermal treatment of substrates are known, as well as apparatuses for determining the temperature of a substrate during a thermal treatment thereof.
A known method for the thermal treatment of semiconductor substrates includes for example heating the substrate by means of electromagnetic radiation, which is emitted by lamps, such as tungsten halogen lamps. It is known to determine the temperature of the semiconductor wafer via a radiation detector directed onto the substrate for controlling the temperature of the thermal treatment. Since the radiation detector, however, typically not only detects radiation which is emitted from the semiconductor wafer but also radiation which is reflected by the semiconductor wafer or is transmitted there through, a differentiation of these different fractions of the radiation is required for determining the temperature.
For such a differentiation, U.S. Pat. No. 5,318,362, describes the so called Ripple technique, in which a frequency is impressed into the lamp radiation via a respective excitation of the lamp. This was initially achieved by utilizing the AC frequency of the power supply and this technique was refined over time and different frequencies were impressed. Changes in the temperature of the semiconductor wafer occur substantially slower in comparison to the impressed frequency. Thus, the radiation emitted by the semiconductor wafer due to its own temperature does not contain the frequency impressed onto the lamp radiation and may thus be differentiated there from.
For determining the temperature of the substrate with this technique, initially the emissivity of the substrate has to be determined and subsequently the temperature. The degree of emissions or emissivity of an object may depend on its temperature or process reactions and may change during the thermal treatment. Such a change may be gradual or erratic, and the change may be reversible or may be permanent. In particular, erratic changes may lead to an error in the determination of the temperature, if the change is detected too slowly or not at all. Calibration of an emissivity measurement is often difficult, since stable references are lacking. Furthermore, the emissivity of an object may also depend on the surroundings and may be different on the inside of a reactor compared to the outside thereof.